Python Lambda, filter, reduce and map

1. Lambda

The lambda operator or lambda function is a-to-create small anonymous functions, i.e. functions without a name.

It is convenient to create a function. Like what

　　

def add (x, y): Return x+y

Using Lambda to write is

　　

Lambda X,y:x+y

Very concise. This statement returns a function pointer, which you can assign, or coordinate with the map, reduce, and so on.

For example, if you want to multiply each value of list [1,2,3,4,5] by 2, return a list.

2. Map

Lambda with map is the most convenient.

R = Map (func, seq)

Map receives a func pointer and then functions to each member of the SEQ.

The example above is:

　　

Map (Lambda x:x*2,[1,2,3,4,5])
[2, 4, 6, 8, 10]

　　　　

3. Filtering

Similar to map, except that he filters the list and accepts a Func lambda expression, and then filters out if the expression is true.

Filter (function, list)

　　

FIB = [0,1,1,2,3,5,8,13,21,34,55]filter (lambda x:x% 2, fib) [1, 1, 3, 5, 13, 21, 55]

Filters out even-numbered items directly.

4.Reducing

The function reduce (func, SEQ) continually applies the function func () to the sequence seq. It returns a single value.

If seq = [S1, S2, S3, ..., SN], calling reduce (func, seq) works like this:

[Func (S1, S2), S3, ..., SN]

[Func (Func (S1, S2), S3), ..., SN]

The func operation of the list is continued, resulting in a numeric value!

　　

Reduce (lambda x,y:x+y, [47,11,42,13]) 113

This, for example, adds to the 47,11 in turn to [58,42,13]

And then add [100,13]

113

　　

Python Lambda, filter, reduce and map